Known characteristic-impedance transformers are used for evenly dividing in a matched and thus reflection-free manner RF energy supplied via an incoming coaxial line among two or more outgoing coaxial lines having the same characteristic-impedance as the incoming coaxial line, which as a rule is 50Ω. Such characteristic-impedance transformers are also known as distributors or splitters. They usually comprise several transformation stages, each of which includes a coaxial line section having a mechanical length of approximately λ/4 (λis the wavelength of the operating or center frequency). A software known as APLAC®, which is available on the market from AWR Corp (El Segundo, Calif.), can be used for calculating the precise length and the diameter of an inside conductor and an outside conductor of the line sections. For reasons of brevity, the individual line sections will therefore be referred to below and in the claims as λ/4 lines.
In principle, a characteristic-impedance transformer should be as free as possible from reflections, i.e., it should have a low VSWR (voltage standing wave ratio), especially at the first terminal. However, VSWR values that are acceptable at adequate bandwidth require at least three transformation stages, and four or more stages when large bandwidths are required simultaneously. Since the transforming line sections are disposed in series, not only electrically but also mechanically, known characteristic-impedance transformers are constructed to be of a large length. Their (theoretical) length is at a minimum equal to n·λ/4, i.e., proportional to the number n of the transformation stages.